Clean up POST dossier endpoint

[himynamesdave]

Dossier should have

report_ids (array): ids of Report objects you want to add to dossier name: name of the dossier description: description of the dossier created_by_ref (valid stix identity object json): assigned as owner of dossier tlp_level (use STIX2 TLP levels -- same as files): tlp level of dossier labels (array of alphanumeric chars): labels to be attached to dossier

[fqrious]

You asked me to remove tlp_level in #18, should I really add it back?

[himynamesdave]

@fqrious i am designing Stixify web, and realised its needed. Sorry to make you go back and do this, but yes, needed